The eye of a mammal is composed of a cornea, or clear outer tissue, which refracts light rays en route to the pupil, an iris which controls the size of the pupil, thus regulating the amount of light entering the eye, and a lens which focuses the incoming light through the vitreous fluid to the retina. The lens is embedded in a capsular bag. In the perfect eye, the light path from the cornea, through the lens and vitreous fluid to the retina is unobstructed. Any obstruction or loss in clarity within these structures causes scattering or absorption of light rays, resulting in diminished visual acuity. For example, the lens is susceptible to oxidative damage, trauma and infection.
As the body ages, the effects of oxidative damage accumulate, resulting in loss of lens flexibility and in denatured proteins that slowly coagulate, reducing lens transparency. The natural flexibility of the lens is essential for focusing light onto the retina by the process of accommodation. Accommodation allows the eye to adjust the field of vision for objects at different distances.
Lenticular cataract is a lens disorder resulting from the further progression of protein coagulation and calcification. There are four common types of cataracts: senile cataracts associated with aging and oxidative stress, traumatic cataracts which develop after a foreign body enters the lens capsule or following intense exposure to ionising radiation or infrared rays, complicated cataracts which are secondary to diseases such as diabetes mellitus or eye disorders such as detached retinas, glaucoma and retinitis pigmentosa, and toxic cataracts resulting from medical or chemical toxicity. Regardless of the cause, the disease results in impaired vision and may lead to blindness.
Treatment of such severe lens diseases requires surgical removal of the lens from the capsular bag. The surgical procedure typically involves phacoemulsification, followed by irrigation and aspiration. Implantation of an intraocular lens (IOL) following the extraction of a cataract is now a standard ophthalmic procedure. Current IOL:s include rigid, non-deformable lenses as well as rollable or foldable lenses. Furthermore, techniques wherein a low viscosity lens material is directly injected into the empty capsular bag and cured in situ as part of the surgical procedure to form an IOL, reducing surgical incisions to about 1 mm, have been suggested. In such a process the capsular bag is used as a mould to form the shape of the lens and thereby contribute to control its refraction.
In connection with the procedures described above for replacement of the natural lens with an implant, there may arise complications. Some of these complications are characterized by a migration of epithelial cells within the capsule, which form a cell layer occluding the lens.
Prevention of cell migration has been addressed by different investigators. Thus, it has been discovered that implantation of an IOL having sharp edges into rabbit eye lens capsules, such that the edges of the lens contact the inside of the capsular bag, leads to inhibition of migrating lens epithelial cells (Nishi et al, ophthalmic Surg Lasers 29:587–594 (1998); Nishi and Nishi, J Cataract Refract Surg 25:521–526 (1999); Nishi et al, J Cataract Refract Surg 26:1543–1549 (2000)). The problem of epithelial cell migration is also addressed in U.S. Pat. No. 6,319,282, in the context of using capsular equator rings for maintenance or establishment of an extended capsular diaphragm. U.S. Pat. No. 6,319,282 describes a capsular equator ring having sharp edges for the inhibition of migration of subcapsular epithelium cells. None of the above documents mention the problem of prevention of epithelial cell migration in connection with injection of lens-forming materials into the capsule. The injection of a lens-forming material into the capsule, which material subsequently forms, through curing thereof in situ or otherwise, an intraocular lens, poses additional problems as regards the migration of epithelial cells. This is so because of the fact that the lens formed will completely fill the lens capsule, and in particular will not be removable in the manner of previously used flexible or non-flexible IOL:s. Thus, the problems posed by epithelial cell migration are more severe and difficult to address in the context of injected, lens-forming materials than in the situations described by previous workers in the field.